The present invention relates to an image display apparatus for displaying an image in accordance with a television image signal or the like and a driving method thereof and, more particularly, to an image display apparatus having an electron source with a plurality of electron-emitting devices and a fluorescent substance for emitting light upon reception of electrons emitted by the electron source, and a display control method in the apparatus.
Conventionally, two types of devices, namely thermionic and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction emission type electron-emitting devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
A known example of the surface-conduction emission type electron-emitting devices is described in, e.g., M. I. Elinson, xe2x80x9cRadio E-ng. Electron Phys., 10, 1290 (1965) and other examples will be described later. The surface-conduction emission type electron-emitting device utilizes the phenomenon that electrons are emitted by a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction emission type electron-emitting device includes electron-emitting devices using an Au thin film [G. Dittmer, xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)], an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)], a carbon thin film [Hisashi Araki et al., xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 24 is a plan view showing the device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction emission type electron-emitting devices. Referring to FIG. 24, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 24. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 24 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction emission type electron-emitting devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In forming processing, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after forming processing, electrons are emitted near the fissure.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenium conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
FIG. 25 is a sectional view showing the device by C. A. Spindt et al. described above as a typical example of the FE type device structure. In FIG. 25, reference numeral 3010 denotes a substrate; 3011, an emitter wiring made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, a gate electrode. In the FE type device, a voltage is applied between the emitter cone 3012 and gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012.
As another FE type device structure, there is an example in which an emitter and gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of FIG. 25.
A known example of the MIM type electron-emitting devices is described in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961). FIG. 26 shows a typical example of the MIM type device structure. In FIG. 26, reference numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 100 xc3x85; and 3023, an upper electrode made of a metal and having a thickness of about 80 to 300 xc3x85. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper and lower electrodes 3023 and 3021 to emit electrons from the surface of the upper electrode 3023.
Since the above-described cold cathode devices can emit electrons at a temperature lower than that for thermionic cathodes, they do not require any heater. The cold cathode device has a structure simpler than that of the thermionic cathode and can shrink in feature size. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the thermionic cathode is low because thermionic cathode operates upon heating by a heater.
For this reason, applications of the cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the surface-conduction emission type electron-emitting devices have a simple structure and can be easily manufactured, and thus many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of the surface-conduction emission type electron-emitting devices to, e.g., image forming apparatuses such as an image display apparatus and image recording apparatus, charge beam sources, and the like have been studied.
Particularly as an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant, an image display apparatus using a combination of a surface-conduction emission type electron-emitting device and a fluorescent substance which emits light upon irradiation of an electron beam has been studied. This type of image display apparatus using a combination of the surface-conduction emission type electron-emitting device and fluorescent substance is expected to exhibit more excellent characteristics than other conventional image display apparatuses. For example, compared with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require any backlight because it is of a self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the present applicant. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat panel display reported by R. Meyer et al. [R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)].
An application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the present applicant.
The present inventors have examined cold cathode devices of various materials, various manufacturing methods, and various structures, in addition to the above-mentioned cold cathode. Further, the present inventors have made extensive studies on a multi electron-beam source having a large number of cold cathode devices, and an image display apparatus using this multi electron-beam source.
The present inventors have examined a multi electron-beam source having an electrical wiring method shown in, e.g., FIG. 27. That is, a large number of cold cathode devices are two-dimensionally arranged in a matrix to obtain a multi electron-beam source, as shown in FIG. 27.
Referring to FIG. 27, numeral 4001 denotes a cold cathode; 4002, a row-direction wiring; and 4003, a column-direction wiring. The row- and column-direction wirings 4002 and 4003 actually have finite electrical resistances, which are represented as wiring resistances 4004 and 4005 in FIG. 27. This wiring method is called a simple matrix wiring method.
For the illustrative convenience, the multi electron-beam source is illustrated in a 6xc3x976 matrix, but the size of the matrix is not limited to this. For example, in a multi electron-beam source for an image display apparatus, a number of devices enough to perform a desired image display are arranged and wired.
In a multi electron-beam source in which cold cathode devices are arranged in a simple matrix, appropriate electrical signals are applied to the row- and column-direction wirings 4002 and 4003 to output a desired electron beam. For example, to drive cold cathode devices on an arbitrary row in the matrix, a selection voltage Vs is applied to a column-direction wiring 4002 on a row to be selected, and at the same time, a non-selection voltage Vns is applied to row-direction wirings 4002 on unselected rows. In synchronism with this, a driving voltage Ve for outputting an electron beam is applied to the column-direction wirings 4003. According to this method, when voltage drops across the wiring resistances 4004 and 4005 are neglected, a voltage (Vexe2x88x92Vs) is applied to the cold cathode device on the selected row, and a voltage (Vexe2x88x92Vns) is applied to the cold cathode devices on the unselected rows. When the voltages Ve, Vs, and Vns are set to appropriate levels, an electron beam having a desired intensity must be output from only the cold cathode device on the selected row. When different driving voltages Ve are applied to the respective column-direction wirings, electron beams having different intensities must be output from respective cathodes on the selected row. A time for outputting an electron beam can be changed by changing a time for applying the driving voltage Ve.
A multi electron-beam source obtained by arranging cold cathode devices in a simple matrix has a variety of applications. For example, when an electrical signal corresponding to image information is appropriately applied, the multi electron-beam source can be applied as an electron source for an image display apparatus.
As described above, a desired beam output can be obtained by applying a driving voltage and performing pulse width modulation. In some cases, however, a desired beam output fails to obtain owing to the voltage drop caused by the wiring resistances 4004 and 4005. To prevent this, the electron source adopts a method of supplying a current value corresponding to the voltage (Vexe2x88x92Vs) from a current source to the cold cathode. According to this method, a desired voltage can be applied to each cold cathode device regardless of the voltage drop caused by the wiring resistances 4004 and 4005.
A color display apparatus, which uses such electron source and a fluorescent substance for emitting light upon reception of electrons from the electron source, comprises fluorescent substances corresponding to, e.g., R, G, and B colors. These fluorescent substances are driven in accordance with an input image signal to display a color image corresponding to the input image signal. However, if the color tone of a color image to be displayed is changed by the user or the like, this color display apparatus cannot display a color image in colors of user tastes by simple color adjustment.
The present invention has been made in consideration of the above situation, and has as its object to provide an image display apparatus for performing color adjustment by controlling the electron-emitting amount from electron-emitting devices which drive emission substances of respective colors, and a display control method in the apparatus.
It is another object of the present invention to provide an image display apparatus which has voltage sources in correspondence with driving sources for emission substances of respective colors, and performs color adjustment by controlling the output voltage of each voltage source to control the electron-emitting amount for driving the emission substances, and a display control method in the apparatus.
It is still another object of the present invention to provide an image display apparatus which has current sources in correspondence with driving sources for emission substances of respective colors, and performs color adjustment by controlling the output current of each current source to control the electron-emitting amount for driving the emission substances, and a display control method in the apparatus.
It is still another object of the present invention to provide an image display apparatus which has emission substances of respective colors laid out in stripes, and adjusts display colors by adjusting charges applied to the emission substances of the respective colors in accordance with designated color adjustment.
To achieve the above objects, an image display apparatus according to the present invention comprises the following arrangement.
That is, an image display apparatus comprises
an electron source having a plurality of electron-emitting devices,
emission means, having emission substances corresponding to respective colors, for emitting light upon reception of electrons emitted by the electron source, thereby displaying a color image,
modulation means for outputting a pulse signal having a pulse width corresponding to an image signal, and
voltage control means for controlling a voltage of the pulse signal for driving each of the electron-emitting devices for irradiating the emission substances corresponding to the respective colors with electrons.
Alternatively, an image display apparatus comprises
an electron source having a plurality of electron-emitting devices,
emission means, having emission substances corresponding to respective colors, for emitting light upon reception of electrons emitted by the electron source, thereby displaying a color image,
modulation means for outputting a pulse signal having a pulse width corresponding to an image signal, and
current control means for controlling a current of the pulse signal for driving each of the electron-emitting devices for irradiating the emission substances corresponding to the respective colors with electrons.
The current control means desirably comprises a current source for outputting a current corresponding to an application voltage, and voltage control means for controlling the application voltage.
The voltage control means desirably controls the application voltage in accordance with an adjustable input voltage and a reference voltage corresponding to each of the plurality of electron-emitting devices.
It is desirable that the image display apparatus further comprise instruction means for instructing adjustment of a display color, and the voltage control means control the voltage of the pulse signal in accordance with an instruction from the instruction means.
It is desirable that the plurality of electron-emitting devices be laid out in a matrix, and the emission substances corresponding to the respective colors be laid out in stripes in units of colors.
The image display apparatus desirably further comprises scanning driving means for selecting respective scanning lines of the plurality of electron-emitting devices, and applying a predetermined voltage to the selected scanning lines.
The pulse signal output from the modulation means is desirably input to a column wiring of the matrix.
The emission substances corresponding to the respective colors are desirably R, G, and B fluorescent substances.
The electron-emitting device is desirably a cold cathode device.
The electron-emitting device is desirably a surface-conduction emission type electron-emitting device.
The electron-emitting device is desirably an FE type electron-emitting device.
The electron-emitting device is desirably an MIM type electron-emitting device.
Alternatively, an image display apparatus comprises
a display panel in which devices are arranged at or near intersections of modulated-signal wirings and scanning wirings, and devices connected to a common modulated-signal wiring emit light of the same color,
a control voltage source for supplying an adjustable control voltage corresponding to each color of light emitted by the display panel,
a variable current source which is connected to the modulated-signal wiring, receives from the control voltage source a control voltage corresponding to a color of light emitted by devices connected to the modulated-signal wiring, and outputs a current corresponding to the control voltage to the modulated-signal wiring, and
a modulated-signal driver for modulating the current output from the variable current source into a pulse having a width corresponding to an image signal value.
It is desirable that the control voltage source include a first voltage source for outputting a first voltage adjustable by an operator and a second voltage source for outputting a second voltage corresponding to correction data for correcting an input/output characteristic of each device, and output a voltage adjusted by the second voltage based on the first voltage.
It is desirable that the display panel have elementary colors laid out in stripes in units of modulated-signal wirings, and the control voltage source be independent for each elementary color.
It is desirable that the display panel comprise a fluorescent plate of colors corresponding to the respective devices, and emit light upon collision with an electron beam emitted by the device.
The device is desirably a cold cathode device.
The device is desirably an electroluminescent device.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.